The stakes are high for the GOP's national push for the Senate majority this fall as well as for Brown's own political ambitions.

The longtime Massachusetts resident, having recently relocated to his seacoast New Hampshire vacation home, spent much of the past two weeks calling key New Hampshire Republican officials and influential GOP activists, indicating that he was likely to run and seeking their support. At the same time, Brown's camp has quietly begun offering paid positions to Republican operatives for a prospective New Hampshire campaign.

Several people involved in the discussions believe that Brown has decided to run, but there remains a healthy dose of skepticism given the former Republican senator's recent track record. The 54-year-old Brown angered Massachusetts Republicans last year after indicating he would run in the state's special U.S. Senate election, only to change his mind late in the process.

"He's been reaching out to opinion leaders, to grassroots activists, getting a sense of, 'Would you be supporting a Scott Brown campaign,'" said former New Hampshire Rep. Frank Guinta, who is running again for Congress and was included in Brown's outreach efforts. "That, to me, says he's serious. But I think only Scott Brown knows if Scott Brown is going to run."

Democrats hope he does not.

While recent polls give Shaheen a solid lead in a prospective matchup, Brown's near-universal name recognition in a state that shares a media market with Massachusetts and his national fundraising network would make him a serious contender on Day One should he enter the race.

Shaheen, a former governor, was widely expected to win her first re-election test in November before Brown began hinting late last year that he might cross state lines to challenge her. National Democrats already have their hands full defending more vulnerable Democratic incumbents across the country as they fight to retain their six-seat Senate majority.

With finite resources, they would rather not devote additional time or resources to a New Hampshire seat that was supposed to be safe.

But Democrats and their allies are already preparing for a worst-case scenario, having spent roughly $360,000 combined on television advertising against Brown in recent weeks. Conservative critics spent heavily to weaken Shaheen earlier in the year, led by the tea party ally Americans For Prosperity, which spent roughly $700,000 on television ads knocking Shaheen's support for President Barack Obama's health care overhaul.

Initial polls suggested a Brown-Shaheen matchup was essentially a tossup, but surveys conducted more recently after the anti-Brown ads give Shaheen a significant lead.

Whether he runs or not, there are risks for Brown, who is also hinting at a 2016 presidential run. He is set to visit Iowa later in the month.

Some believe Brown's political brand would suffer permanent damage should he ultimately disappoint New Hampshire Republicans by backing out of the Senate race after so much hoopla. But should he run and lose, Brown's resume would be tainted with two high-profile losses in two years.

He shocked the political world and rose to national prominence by winning the 2010 special election to replace the late Massachusetts Sen. Ted Kennedy, but he was soundly defeated in his first re-election test against Sen. Elizabeth Warren in 2012. Despite the urging of Massachusetts Republicans, he declined to run in the state's 2013 special election to replace former Sen. John Kerry, who was tapped to serve as Secretary of State.

The conservative editorial board of the New Hampshire Union Leader, the state's largest newspaper, recently criticized Brown for holding the state party and other GOP candidates "in stasis."

"Even world-class publicity magnets like the Kardashians or Justin Bieber would be impressed by Brown's ability to monopolize media attention on what is, so far, a non-candidacy," the newspaper opined.

Brown has said he will make a decision by April, although it's unclear if that means by the end of March or April. He declined to respond to questions about his timeline this week, although a Brown adviser said a decision would likely come in weeks, not months.

In the meantime, Brown continues his role as a paid contributor for Fox News, renewing his contract less than a month ago. The news network has previously cut ties with Republicans when it became clear they were seriously considering running for office. The network said this week there was no change in its relationship with Brown.

Jamie Burnett, a veteran New Hampshire Republican strategist, called Brown the "one potential candidate for U.S. Senate in New Hampshire that people are genuinely excited and hopeful about."

"People have gotten their hopes up," Burnett said. "They would be disappointed if he didn't run."